1. Field of the Invention
The present invention relates to a contactless power receiving unit employed to obtain necessary power in various electronic devices such as a mobile phone and a personal computer.
2. Description of the Related Art
Various contactless charging units are disclosed in Published PCT application No. JP2005-525705, Japanese Patent Application Publication No. 2006-333557, Japanese Patent Application Publication No. 2005-354197, and the like. Japanese Patent Application Publication No. 2005-354197 discloses a technique of transmitting energy from a primary side power supply unit to a secondary side power receiving unit by a parallel rotating magnetic field.
In a contactless power receiving unit shown in FIG. 12, power supply unit 8 includes AC power source 81, phase control circuit 82, and two power transmitting coils 83. Phase control circuit 82 is configured to divide an AC current provided from AC power source 81 into two current components having a phase difference of 90° from each other. The two components are respectively supplied to two power transmitting coils 83, which thereby cause magnetic fields Bx and By respectively, having a phase difference of 90° from each other. Two power transmitting coils 83 are arranged such that coil axes thereof are orthogonal to each other.
Meanwhile, power receiving unit 9 includes power receiving coil 91 and rectifier circuit 92. Power receiving coil 91 is configured to receive a parallel rotating magnetic field generated in power supply unit 8, and rectifier circuit 92 rectifies the AC power received by power receiving coil 91. The DC power outputted from rectifier circuit 92 is supplied to load 93.
Each of power transmitting coils 83 of power supply unit 8 is configured of multiple rows of conductor wires 14 running parallel on a plane as shown in FIG. 11A, and currents flow in the same direction in these conductor wires 14. With this configuration, a magnetic field is formed so as to surround each conductor wire 14 as shown in FIG. 11B, and magnetic fields of each conductor wire 14 counteract each other between two adjacent conductor wires 14. As a result, parallel magnetic fields are formed to be parallel to a plane in which multiple conductor wires 14 are arranged, as shown in FIG. 1C.
Thereafter, two power transmitting coils 83 are arranged orthogonal to each other, while currents are supplied to two power transmitting coils 83 with 90° phase difference. In this way, the two parallel magnetic fields formed by power transmitting coils 83 are synthesized with each other to form a parallel rotating magnetic field that rotates on the aforementioned plane.
Above-mentioned power supply unit 8 is included in charging pad 80 shown in each of FIGS. 13A and 13B, for example. When power receiving unit 9 is placed on charging pad 80, parallel rotating magnetic field B generated by power supply unit 8 acts upon power receiving coil 91, so that induced electromotive force is generated in this power receiving coil 91. Here, parallel rotating magnetic field B rotates within a plane parallel to charging pad 80. Accordingly, even if power receiving coil 91a is placed on charging pad 80 so as to be rotated by an angle θ, the magnetic field B eventually acts perpendicularly upon power receiving coil 91a by rotation as shown in FIG. 13B. Hence, power can be received regardless of the orientation that power receiving coil 91 is placed.
However, this type of charging unit requires phase control circuit 82 in power supply unit 8 as shown in FIG. 12. Phase control circuit 82 is configured of multiple active circuit elements, which leads to a problem of complication in the circuit configuration.
Moreover, in the case where power receiving coil 91 of power receiving unit rotates by an angle θ, the phase of the amplitude of the voltage induced to power receiving coil 91a is delayed (or preceded, depending on conditions) by θ, as shown by a broken line in FIG. 14. This causes a problem of a difference in charged amounts at arbitrary time points, due to a difference in the amount of induced voltages at the arbitrary time points, depending on the orientation of power receiving coil 91a. 